The invention refers to the field of electronic reproduction technology and is directed to a method and an apparatus for producing circular distributions, particularly color distributions, on a recording medium. For example, the recording medium can be the picture screen of a monitor or a recording material (film).
Circular color distributions are gradual changes of density or color values, whereby at least one identical color value is allocated to the picture elements respectively lying on a circular line (level line) arranged concentrically relative to the center or middle. Circular color distributions, for example, are often employed as backgrounds in reproduction technology, with articles being positioned in front of them. The greatest variety of visual effects can be achieved on the basis of the design of the circular color distributions with respect to the position of the centers as well as the color composition. When producing circular color distributions, one usually proceeds for every picture element such that the distance from the center is first identified in a prescribed reference raster and the corresponding color value is subsequently identified, for example via a table allocation. A significant time requirement arises in a calculation of the respective distance values implemented during the production of the color distributions due to calculations of squares and square roots. This has a negative influence on the speed of the generation of the distribution. Thus, conversion methods have become known which shorten the required conversion time. For example, it is possible to respectively calculate the distance values with the assistance of whole-numbered root algorithms without taking the places following the decimal point into consideration. The losses in precision thereby occurring are usually imperceptible, so that no noticeable reduction in the image quality occurs. The execution of such whole-numbered root algorithms is essentially based on whole-numbered divisions and comparison operations. It is also known to utilize the central symmetry of the circle when producing circular color distributions. When, for example, the color values for a sector of 45.degree. are determined first, then the color information for the entire area can be acquired by mirrorings at the diagonals and the principal axes. The whole-numbered root algorithms can also be utilized in the calculation of the color values for the corresponding circular segment.
These known methods, however, have the disadvantage that the color values for a comparatively large area must still be determined with a complicated calculation. When producing circular color distributions on a recording medium that provides an essentially rectangular recording area, symmetry properties can only be meaningfully utilized when the center of the circular color distribution and the center of the corresponding, rectangular recording area respectively coincide. The time savings in the conversion by utilizing symmetry effects become all the less the greater the distance the centers from one another.
Given a center that lies outside the recording area, it is usually no longer possible to save conversion time on the basis of symmetry properties.
The exploitation of mirror symmetries assumes that a plurality of color values are simultaneously available. This, however, is only possible, particularly given color distributions having a fine resolution, when an image store having high storage capacity is available for the color values. This is often not the case.